It is widely recognized in commercial packing and food processing plants as well as in the paper and pharmaceutical industries, as well as other industries, that cleaning and/or sanitizing of equipment can be greatly enhanced by the use of foam rather than high pressure sprayed water. It is also common for these industries to utilize both portable and/or central clean-in-place systems to achieve and maintain sanitary conditions.
A portable foam cleaner is usually a batch system, one such system being disclosed in U.S. Pat. No. 3,797,744. Utilizing a plurality of tanks, a foam with or without a sanitizer can be generated. The system utilizes compressed air and chemicals under pressure to generate foam through a foam generator.
A central clean-in-place foam system utilizes a continuous process. The foam generating chemical and the sanitizing chemical are usually educted into a large mixing tank along with the water driving the eductor. An automatic level control activates the eductor water source to keep the tank filled at all times. Feed-rates, and thus concentrations and foam characteristics, can be controlled by use of rotometers. From the mixing tank, the solution is pumped under pressure throughout the plant to the individual foam generating stations. A gas, such as compressed air, is introduced at this point to generate the foam. The foam is then delivered through a hose or otherwise conducted to the surfaces to be cleaned and sanitized. U.S. Pat. No. 3,823,727 discloses one type of foam generating station utilized in a central foam system. Many other types are currently on the market.
The foam covers and adheres to the surface to be cleaned. Some cleaning, penetrating and loosening action can occur, depending on the formulation of the foam generating chemical. To achieve microbiological control, a sanitizer, or disinfectant chemical, is used in the foam system.
One of the advantages of using foam to achieve microbiological control is that, since it adheres to the surface and remains for a period of time, it allows more time for the disinfectant to do its work. Although the foam prolongs the contact time, those disinfectants.that have rapid rate of kill are preferred in order to obtain the maximum benefit.
The sanitizing, or disinfectant, chemical is essential in order to obtain the desired destruction of the microorganisms, e.g., bacteria, molds, fungi, spores, and viruses. Common inorganic disinfectants currently in use are exemplified by chlorine and iodine. Examples of organic disinfectants are carbamates or quaternary ammonium compounds. Although the foregoing disinfectants are somewhat effective and are widely used in the current state of the art, they have many limitations. The use of a more powerful, more rapid disinfectant would greatly enhance the sanitizing effectiveness of foam systems.
The use of chlorine dioxide in many disinfection applications is growing widely because of its superior bactericidal, sporicidal, fungicidal, and viricidal properties as well as its extremely fast rate of disinfection. The use of chlorine dioxide in a foa system would greatly enhance the art of sanitizing.
Prior to this invention, the use of chlorine dioxide in foams or foam cleaners for the disinfection of microorganisms wa not known. Chlorine dioxide is irritating and has a very noxious odor at concentrations as low as 0.5 ppm in a water system. Moreover, chlorine dioxide does not undergo hydrolysis so its irritating and noxious properties persist. It was previously thought that it was impossible to use chlorine dioxide in an aqueous foam system at relatively high chlorine dioxide concentrations since its strong, unpleasant odor when dissolved in water makes it impossible to spray at concentrations necessary to achieve sanitization in, for example, food processing plants where personnel are working in the close vicinity.
Another reason that chlorine dioxide has not previously been used in a foam system at relatively high chlorine dioxide concentrations is that it is such a strong oxidizing agent that it was thought that it would destroy or break down the organic compounds that make up the foam generating chemical. Another reason that chlorine dioxide has not previously been used in a foam system is that it was thought that the chlorine dioxide would undergo rapid degradation and lose its disinfectant and biocidal properties.
Surprisingly, the use of chlorine dioxide in a foam system, in accordance with the practice of this invention, does not result in any chlorine dioxide odor at relatively high concentrations up to 1200 ppm. Moreover, it does not destroy the organic foam generating compounds. In effect, if formulated correctly, the chlorine dioxide foam solution of this invention is very stable and produces a foam of exceptionally high quality. In addition, it has been found that chlorine dioxide in foam solutions is very stable and remains potent as a biocide for up to at least 72 hours or even longer.
The term "foam solution" as used herein means an aqueous disinfectant solution containing a foam generating chemical and which is capable of producing a foam when mixed with a gas such as air in, for example, a foam generator. The foam generating chemical is typically one or more surfactants. A suitable surfactant may be cationic, nonionic, or anionic, as long as it is capable of forming an aqueous foam. The choice of surfactant is within the skill of the art. The disinfectant is primarily chlorine dioxide.
Three well known reactions for generating chlorine dioxide from sodium chlorite are as follows: EQU 2 NaClO.sub.2 +Cl.sub.2 .fwdarw.2 ClO.sub.2 +2 NaCl (1) EQU 2 NaClO.sub.2 +HOCl.fwdarw.2 ClO.sub.2 +NaCl+NaOH (2) EQU 5 NaClO.sub.2 +4HCl.fwdarw.4 ClO.sub.2 +5 NaCl+2 H.sub.2 O (3)
Equation (1) exemplifies the generation of chlorine dioxide by the action of an oxidizing agent, i.e., chlorine, on a metal chlorite, i.e., sodium chlorite. Equation (2) exemplifies the generation of chlorine dioxide by the action of an oxidizing acid, i.e., hypochlorous acid, on a metal chlorite. Equation (3) illustrates the production of chlorine dioxide by the action of an acid, i.e., hydrochloric acid, on a metal chlorite. It will be understood that the above reactions are not limited to the metal hlorite, oxidizing agents and acids illustrated and that the choice of reactants is within the skill of the art.
By means of the foregoing reactions, chlorine dioxide may be obtained by, for example, use of a commercially available chlorine dioxide generator and dissolved in the foam solution. A chlorine dioxide generating apparatus is described in U.S. Pat. No. 4,247,531. Alternatively, chlorine dioxide may be generated in the foam solution via one of the above reactions.
U.S. Pat. No. 2,392,936 discloses aqueous oxidizing foam solutions which are taught to be useful in decontaminating areas contaminated with, for example, noxious or poisonous chemicals. The disclosed aqueous foam solutions contain a foam generating soap and an oxidizing agent such as sodium chlorite. It is disclosed that the foregoing solution may be acidified by the addition of hydrochloric acid to a pH of about 4. It has been found that when the pH of such a solution has been lowered to about 4, only about 0.5 percent of the sodium chlorite is converted to chlorine dioxide.